A St. Louis prosecutor on Thursday said she would investigate published allegations that Missouri Gov. Eric Greitens threatened to blackmail a woman with whom he was having an extramarital affair by saying he would distribute a nude photo of her if she revealed the relationship.

“The serious allegations against” Greitens “are very troubling,” said St. Louis Circuit Attorney Kimberly Gardner in a statement. “After further consideration, I have decided to launch a formal investigation into the alleged actions of Governor Greitens.”

“It is essential for residents of the City of St. Louis and our state to have confidence in their leaders,” she said. “They must know that the Office of the Circuit Attorney will hold public officials accountable in the same manner as any other resident of our city. Both parties and the people of St. Louis deserve a thorough investigation of these allegations.”

The alleged actions, which have been denied by Greitens’ lawyer, stem from a report by KMOV in St. Louis which featured a surreptitious recording purportedly of the woman with whom Greitens acknowledges having an affair in 2015. She describes Greitens inviting her to his home and taking pictures of her naked and then threatening to use them against her if she ever mentioned their relationship.

Greitens (R), responding to media reports, acknowledged Wednesday night that he was unfaithful to his wife “a few years ago” before being elected. But his lawyer denied the blackmail allegation.

The lawyer, James F. Bennett, responded to the prosecutor’s statement Thursday, saying the “governor is very confident he will be cleared in any investigation,” according to the St. Louis Post Dispatch. This is a three-year-old personal matter that presents no matters of public or legal interest. The facts will prove that fully.”

The woman, who has not been named publicly, was Greitens’s hair stylist, according to media reports confirmed by The Washington Post with a source familiar with the situation.

A joint statement posted Wednesday night by Greitens and his wife, Sheena, said in part that “a few years ago . . . there was a time when he was unfaithful in our marriage. This was a deeply personal mistake. Eric took responsibility, and we dealt with this together honestly and privately.”

Greitens, 43, is a relatively new star in the Republican Party who boasts an extraordinary résumé: Former Navy SEAL and Lt. Commander, attended Duke University on scholarship; Rhodes scholar at Oxford; PhD, author and White House Fellow during the administration of President George W. Bush. He is the author of “Resilience: Hard-Won Wisdom for Living a Better Life” and, according to a profile in St. Louis Magazine, has had presidential aspirations since he was a young man. His wife, Sheena Chestnut Greitens, is an assistant professor of political science at the University of Missouri, and a nonresident senior fellow at the Center for East Asian Policy Studies at the Brookings Institution in Washington.

Missouri’s first lady, Sheena Greitens, an assistant professor at the University of Missouri, sits for an interview in Columbia. (Luke Brodarick/Missourian via AP)

A Democrat-turned-Republican, Greitens was elected governor in November 2016 after a campaign that emphasized his status as a family man. Greitens and his wife have two children. “I’m Eric Greitens,” he said during the campaign. “I’m a Navy SEAL, native Missourian and most importantly, a proud husband and father.”

The governor had just delivered his state-of-the-state address Wednesday when KMOV in St. Louis broke the story about his affair with his former hairdresser in 2015.

The extramarital relationship itself, however, may have been the least explosive part of the story.

More unusual was what she purportedly said in a recording made surreptitiously by the woman’s jealous ex-husband, which the station played.

In it, she can be heard telling how Greitens invited her to his home in 2015. Once she arrived, he told her he would show her how to do pullups, taped her hands to exercise rings and blindfolded her, all with her consent.

Then, to her shock, she alleged, he snapped photographs of her naked and threatened to distribute the pictures if she revealed the relationship.

On what was supposed to be a banner evening for Greitens, he then was forced to issue the statement with his wife confirming the affair. His wife also issued her own statement:

We have a loving marriage and an awesome family; anything beyond that is between us and God. I want the media and those who wish to peddle gossip to stay away from me and my children.

Neither the governor or his wife said anything about the reported photo shoot or the alleged blackmail threat.

That came in a separate statement by the couple’s attorney, Bennett, who denied the blackmail claim. “There was no ‘blackmail,’ ” lawyer Bennett said in a written statement, “and that claim is false . . . The outrageous claims of improper contact regarding these almost three-year-ago events are a lie.”

The whole story, which had been the stuff of wild rumors for weeks, originated with the spurned ex-husband, who told KMOV that the relationship between Greitens and the man’s then-wife had led to the breakup of their marriage.

Afterward, the ex-husband went on social media calling Greitens a “homewrecker,” according to KMOV. He then tried to go public with his story and with the recording, speaking with both of Missouri’s major newspapers.

The St. Louis Post Dispatch and the Kansas City Star reported that they too had possession of a transcript of the surreptitious recording and had interviewed the ex-husband. Both papers said they had decided against writing a story because the woman declined to be interviewed. Once the governor released a public statement the papers pushed ahead with their stories.

KMOV decided otherwise. Although it said it had no “on-the-record-comment” from the woman, it went with the story Wednesday night under the headline “Blackmail alleged as Governor Greitens admits to extramarital affair” and took credit for prompting Greitens’s statement.

“I am not after anything,” the ex-husband, who was also unnamed, told KMOV. “I am not a part of politics. I am not a part of anything. I just want to move on with my life.”

He claimed to have been contacted by law enforcement authorities as well as members of the media.

Bennett, Greitens’s lawyer, said in his statement that there was nothing about the relationship that “has generated or should generate law enforcement interest.”

Greitens has received mixed reviews in as governor. While campaigning on a platform of cleaning up government, he admitted to the Missouri Ethics Commission that he had violated campaign finance law, according to the Kansas City Star. He was fined $1,000. He and his senior staff have also come under fire for using an app that deletes text messages after they’ve been read, raising concerns about trying to subvert Missouri open records law.

I wanted to share with you some statements that are important in light of news you may have seen tonight.

A statement from James F. Bennett, our attorney:

“The Governor has now seen the TV report that ran tonight. The station declined to provide the tape or transcript in advance of running their story, which contained multiple false allegations. The claim that this nearly three-year old story has generated or should generate law enforcement interest is completely false. There was no ‘blackmail,’ and that claim is false. This personal matter has been addressed by the Governor and Mrs. Greitens privately years ago when it happened. The outrageous claims of improper conduct regarding these almost three-year-ago events are a lie.”

Joint statement from Sheena and I:

“A few years ago, before Eric was elected governor, there was a time when he was unfaithful in our marriage. This was a deeply personal mistake. Eric took responsibility, and we dealt with this together honestly and privately. While we never would have wished for this pain in our marriage, or the pain that this has caused others, with God’s mercy Sheena has forgiven and we have emerged stronger. We understand that there will be some people who cannot forgive — but for those who can find it in your heart, Eric asks for your forgiveness, and we are grateful for your love, your compassion, and your prayers.”

Fred Barbash, the editor of Morning Mix, is a former National editor and London bureau chief for The Washington Post. He has also been an editor at Politico and Reuters, and was the managing editor of CQ Weekly magazine.